Infor LX MRP Run Window Calculator
This calculator takes one measured Infor LX or BPCS MRP run and scales it to a new number of planned items and a new average bill depth. It then checks both a full regeneration and a net change style run against the overnight batch window, after other jobs.
Your numbers
From job log start and end timestamps
Start-up, clear-down and report steps that do not scale with items
Your results
This is a linear rule of thumb for capacity planning, not an Infor formula. Real run time also depends on CPU, memory, disk, journaling, record locks and concurrent jobs. Measure again after any hardware, release or parameter change.
MRP run time vs planned items
Sweeps Planned items now or in future from 20000 to 120000, holding your other inputs fixed.
Send us your MRP job history for a reviewed estimate
Share several weeks of MRP start and end times with item counts, and we will return a trend and a projection you can take to IT planning.
Optional. The tool and every export work without this. No spam.
How to use it
Get the start and end timestamps of a recent full MRP run from the job log or your scheduler history, and enter the elapsed minutes. Enter the number of items MRP planned in that run, then the item count you expect now or after an acquisition, new product line or site merge. If your bills are getting deeper, for example because subassemblies are being split out, raise the BOM levels now value. Estimate what share of items changes on a typical day for net change. Finally, enter the window you have and the minutes taken by other jobs such as period-end, interfaces, backups and saves.
The method and its basis
The calculator subtracts fixed overhead from the measured run to get variable minutes per planned item. It then scales linearly by item count and by the ratio of average BOM levels, because MRP explodes requirements level by level. A net change run is modelled as the same per-item cost applied to only the share of items that changed. This is a practitioner rule of thumb: planning time grows roughly in line with planned items and depth when hardware and parameters stay the same. It is not an Infor formula. It works best for moderate changes, and you should re-measure after any big change.
- per item = (measured minutes - overhead) / measured items
- regeneration = overhead + per item x new items x (new levels / old levels)
- net change = overhead + per item x new items x changed % x depth factor
- slack = window - other jobs - MRP run
Worked example and how to read it
With the defaults, the measured run takes 180 minutes for 40,000 items, including 10 minutes of overhead, so each item costs 0.00425 minutes. At 55,000 items and the same depth, a full regeneration projects to about 244 minutes. Net change at 15 percent projects to about 45 minutes. With a 240-minute window and 60 minutes of other jobs, 180 minutes are left. Regeneration overruns by about 64 minutes, while net change has plenty of room. A common response is to run net change nightly and schedule full regeneration at the weekend, when the window is longer.
Regeneration vs net change on LX
A full regeneration replans every item and rebuilds the plan from scratch. It clears drift caused by changed lead times, bills, routings, planning parameters and manual changes. A net change run replans only items affected by changes since the last run, so it is much faster, but small errors can build up over time. Check your release's MRP generation options to see which modes your site runs. Most planners still schedule a regular full regeneration, for example weekly or before a key planning meeting. Lock contention also matters: interactive order entry during MRP can stretch the run beyond what this linear estimate shows.
Frequently Asked Questions
How long should Infor LX MRP take?
There is no standard figure. Run time depends on planned items, bill depth, horizon, hardware and other jobs. Measure your own runs from job log timestamps and use this calculator to scale them. Track the trend monthly so you see overruns coming before they hit the morning shift.
Does Infor LX support net change MRP?
BPCS and LX sites commonly run both full regeneration and a faster net change style run. The exact options depend on release and setup, so check the MRP generation options and Infor documentation for your release. This tool models both modes so you can compare them against the window.
Why does BOM depth matter for MRP run time?
MRP calculates requirements level by level. Each extra level means more dependent demand records to explode, net and plan. The calculator uses the ratio of average levels as a simple multiplier, which is an approximation. Very deep or uneven bills can add more time than this linear estimate shows.
What can I do if regeneration no longer fits?
Common options are to run net change on weeknights and regeneration at weekends, move other jobs out of the window, shorten the planning horizon for low-value items, archive old orders, or add CPU and memory. Re-measure after each change rather than relying on the estimate.
If you want planners to ask why MRP suggested an order, in plain English on your own LX data, we can set up a private assistant that reads the same files.
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